One-way or anti-back flow valves are used in many different applications and have many different forms. One such application is as a valve for preventing the back flow of air into passenger vehicle cabins. The valve both seals the cabin against the entry of poisonous fumes and the like, and vents the cabin to prevent or relieve an undesired increase of pressure therein. Such pressure increases can be caused by the operation of the heating, ventilating and air conditioning system, or by the slamming of a door of a vehicle when all of the windows are rolled up. Valves designed to serve as cabin air exhausters must both seal against back pressure, permitting very little air to leak into the cabin, and must open at very low cabin pressure to prevent or quickly reduce any significant increase in cabin pressure. Standards for acceptable flow rates are established by automotive companies.
Cabin air exhausters are typically spring or gravity operated flapper valves, with the flapper being formed of a relative soft rubber or rubber-like material. The flappers are hinged along a top edge in some manner, and hang vertically responsive to gravity. Back pressure tends to force the flappers against the supporting plate. Elevated cabin pressure pushes the flapper away from the plate, allowing cabin air to escape. One problem with such valves is that the desired level of sealing is difficult to consistently achieve. A limitation of valves relying exclusively on gravity to close is that gravity biased valves are sensitive to orientation. The valves must typically be oriented in an upright position on a vertical surface to operate. Another concern is that the flapper may flutter, creating undesired noise when open when air is passing through at a high rate of flow. If a spring is used to provide a more positive closing of the flapper than is possible with gravity, the cabin pressure needed to initiate exhausting will be undesirably increased.
Another common application of one-way or anti-backflow valves is as an exhalation valve for a filter mask. The term “Filter Mask” is meant to describe a device adapted to be worn over the nose and mouth. These filter masks utilize filter material for the removal of unwanted components from the inspired air. One-way valves used in filter masks allow for a relatively unrestricted flow of exhalate out of the mask, while preventing intake under certain conditions. The one-way valves open under the pressure differential upon exhalation of the user. Typical valves in filter masks are of the type which only ensures sealing when in an upright orientation.
It is desired to provide a one way valve which seals effectively against back flow from a first side while opening at relatively low positive pressures on the second side independent of orientation.